This invention relates generally to the separation of fluids from mixtures thereof and, more particularly, to the separation of vapor and liquid from mixtures of the same.
In natural-circulation vapor generators, mixtures of steam and water rise in heated, steam-generating tubes and discharge into one or more large steam drums disposed above the tubes, with the separation of water from steam occurring in separators within the drum. The separated steam is removed through openings in the upper portion of the drum, while the water remaining in the drum is recirculated through downcomers, through the boiler and back to the steam-generating tubes.
Trouble-free operation of a natural-circulation vapor generator requires efficient separation of steam and water and an adequate and properly-distributed supply of water through the steam-generating tubes. The separator, accordingly, has two essential functions, one of which is the separation of water from steam to provide the downcomers with the steam-free water necessary for proper operation of the circulation system of the vapor generator. The other function is the separation of moisture from the steam to provide high-purity steam.
The pressure drop of the circulating fluid through the separator is an important consideration in that this loss must be minimized to maintain proper circulation in the system. Low pressure industrial boilers of present day design are, in general, more highly rated, and efficient separation in the drum, with minimal pressure loss, is essential to furnish steam of the required purity to the point of use and steam-free water to the circulation system. In the circulation of the steam-water mixture through the steam drums and through the steam-water separators located within these drums, the steam-water mixture is generally introduced into a receiving chamber within the steam drum, and through a plurality of inlets into one or more separators. The expansion of the mixture through the separator inlets results in a substantial pressure drop, which if too large can adversely affect the circulation system. Also, at low pressure the steam specific volume is high, and a centrifugal separator for this application must have sufficient flow area to minimize pressure loss and still achieve separation.
Some separators of the prior art have generally been of complicated, S-shaped structures which are expensive and difficult to fabricate. Additionally, the convoluted passages through which the steam-water mixture must flow present another source of pressure loss.